The biggest problem with FDE is that as long as you're using the encrypted computer, FDE isn't protecting you. It doesn't take technical capabilities to exploit this; you just wait until the target has their laptop open to do the interdiction.

FDE's not worthless. Again, I don't think it's even optional; one of your laptops is eventually going to get stolen, and you're going to want the reassurance that at the very least, once it loses power, the thief won't have access to your data (meaning, in effect, that most thieves will never have access to your data). And it's somewhat more powerful on phones, which have integrated designs to make FDE more granular.

But the idea that of all the things the USG could spend energy on, aftermarket FDE software would be their target? It's not very plausible.